Conventionally, there is known a method for producing a three-dimensionally shaped object (hereinafter simply referred to as a “shaped object”) by irradiating a light beam on a specified portion of a powder layer of an inorganic or organic powdery material and sintering or melting the specified portion of the powder layer to form a solidified layer, forming a new powder layer on the solidified layer, irradiating the light beam on a specified portion of the new powder layer to form a new solidified layer and repeating the afore-mentioned steps.
Also known in the art is a method for producing a shaped object by placing a substrate on a vertically movable shaping table, forming a powder layer on the substrate and sintering the powder layer (see, e.g., Japanese Patent Laid-open Publication No. 8-281807). FIG. 9A schematically shows the cross section of a metal optical shaping machine (hereinafter simply referred to as an “optical shaping machine”) used in such a production method. FIG. 9B illustrates the cross section of a shaped object produced by the optical shaping machine. A substrate 41 is installed on a vertically movable table 43. A powder layer 21 is formed on the substrate 41. A light beam L is irradiated on a specified portion of the powder layer 21 to sinter the same into a solidified layer 22. The solidified layers 22 thus formed are laminated to produce a shaped object 3.
In the shaped object production method disclosed in Japanese Patent Laid-open Publication No. 8-281807, however, the shaped object 3 is shrunken when it is cooled after being heated by sintering. This generates a tensile stress by which the surface of the substrate 41 bonded to the shaped object 3 is pulled toward the center. The peripheral portion of the substrate 41 is bent upwards by the upward bending moment F2 caused by the tensile stress. This may possibly render the shape of the shaped object 3 poor if the substrate 41 is not removed from the shaped object 3 after the shaping operation but used as a part of the shaped object 3.